Hello Tiago=2C

You show an Artifact just over 1Hz.

I have a similar artifact which seems related to
air conditioner noise in the ground.

But the artifact which bothers me is much more pure
in frequency and is only present when the machine is running.

I have vehicle noises 3Hz and over.
They vary all the time.

If you are like me=2C you are 800feet over bedrock which
means no roads should be within 800 ft of your
geophone. Impossible for me to do.

But the Air Conditioners in the buildings around me
as well as my own causes terrible artifacts which can
Jam out all other frequencies by overloading
the preamp driving it into saturation or cutoff.
My air conditioner rests upon the ground.
Living in the desert without an air conditioner
is almost unthinkable to computer people
unless you have a cray supercomputer.
(They got their own way to keep cool.)

I fight these artifacts in two ways.

1. Filter Low Pass n=3D1 at 12 second period.
2. Filter again n=3D1 low pass at geophone f0 of 1.0Hz to 1.75Hz.
3.Antialize LP n=3D4 at like 4 to 10 Hz.
4. use sample rate of 100Hz

Another way which seems to help but i do not like
is to dampen very heavily and compensate with
a N=3D1 LPF at like 12 seconds.
If you do this you need more gain=2C like 50Dbv more.

The way to look at noise is to pass your geophone signal
straight through to the A/D with no filtering
and only amplify to like -6.0Dbv the pure noise.

Then make recording samples over 24 hours.

Convert the 1Hr samples to Wave and look at the profiles in
Audacity. You need a FFT program which shows
changes with time so you can see if the
artifacts are constant or variable.

The FFT within Winquake is just an overall profile
and building a waterfall from it is kind of hard.

Audacity is free=2C and I or possibly another PSN person
can supply you with a PSN to WAVE converter program.
This all hinges on the fact you are an amateur and not a
commercial person. Trying to make a living doing this.
These programs like Audacity are generally not free
to commercial enterprises generating revenue.
The people who write these programs want a
so to speak piece of the action.

My current setup is not exactly as I say here.
I am always looking for something better.

Good luck.

Regards=2C
geoff



On 8/9/2012 2:05 AM=2C Tiago A. wrote:
> Forgot the picture to compare noise before/now:
>
> http://dl.dropbox.com/u/15802004/com.png
>
> 2012/8/9 Tiago A. >
>
>     Thanks for the answer Geoff.
>
>     I=B4m not using Larrys Boards (yet)=2C im using a ADC ADS1211P mounte=
d
>     in a PCB=2C image:
>     http://imageshack.us/photo/my-images/31/adca.jpg/
>
>     The board worked ok for almost a year.
>
>     Hadnt much time to test more the noise=2C but here is a picture
>     which shows very well the issues:
>     First image - 3 months back. 0.25Hz to 0.75Hz is ocean noise.
>     Second image - Taken few minutes ago.
>
>
>     >10s noise is probably 10 times higher than before=2C also i have
>     some high count at a specific frequencies=2C starts at +-1Hz=2C next
>     day 2Hz=2C next day 3Hz). Restart the board/Amaseis=2C the high count
>     returns to +-1Hz.
>
>     I will follow your advices and i will search some noise sources.
>
>     Best Regards=2C
>     Tiago.
>
>
>     2012/8/8 GMVoeth GM >
>
>         Sorry Tiago=2C
>
>         I can not now handle SAC files.
>
>         The only kind of files I handle are PSN.
>
>         I recommend you change sample rates=2C Assuming you are using
>         Larrys Type III A/D board.
>
>         Then you create a test file=2C convert to WAVE both before and
>         after sample rate change files.
>
>         Then look at the results in Audacity FFT Waterfall program.
>
>         This is the only way i know how to evaluate such a problem.
>
>         You talk about things I know nothing about like (sample rate
>         to 125sps (-3dB at 36Hz)).
>
>         (-3dB at 36Hz) means to me a Low Pass Filter At 36Hz.
>
>         If you filter at 36 hZ your sample rate should be much higher
>         than 100
>         more like 500 sps.
>
>         You need to filter out even frequencies above the rolloff.
>
>         When you mix frequencies you get the following=2C
>
>         F1 & F2 (Fundamentals)=2C
>          F1 + F2 (SUM)=2C and=2C
>          F1 - F2 (Difference).
>
>         You will notice small variations in the fundamentals
>         can result in large changes at higher harmonics.
>
>
>
>         I am assuming that when you get alizing you are getting these
>         mixing products.
>
>         Frequency mixing is typical for superhetrodyne receivers.
>
>         If your problem is not mixing you need to
>         look at everything else like staic electricity=2C
>         Commom mode rejection=2C Thermal variations.
>
>         Like take a soda straw and carefully blow your warm breath on
>         various components to see what causes changes.
>         Do this while recording.
>
>         It took me a long time to get rid of most artifacts.
>
>         The best thing I did was buy a manufactured (used) geophone
>         then lower the overall gain of my system.
>
>         If you need more than x10000=2C little problems can easily be
>         big ones.
>
>         I was unable to stop unwanted artifacts if gain was over X100=2C0=
00.
>
>         Good Luck Comrade=2C
>         Regards=2C
>         geoff
>
>
>
>
>         On 8/2/2012 4:19 PM=2C Tiago A. wrote:
>
>             Hi Geoff.
>
>             Increasing the sample rate to 125sps (-3dB at 36Hz)=2C
>             didint solve the
>             issue and increased the >10s noise..i will try to increase
>             more the
>             sample rate. But increasing the sample rate reveals a very
>             high count at
>             50Hz=2C i check the earth connections it looks all ok..if i
>             remove the
>             geophone from the ADC=2C i have +-2 counts of noise at
>             16bits and the 50Hz
>             spike is gone. Simply touching a wire from earth in any
>             part of the
>             geophone=2C will make the geophone stiff=2C without respondin=
g.
>
>             SAC file with 15minutes at 125SPS
>             http://dl.dropbox.com/u/15802004/aa.sac
>
>             Netherless the 50Hz issue=2C getting only 3800ohm from a
>             5500ohm geophone
>             is a good indicator that something is wrong with the
>             geophone itself. It
>             still responds ok to >0.1Hz=2C but <0.1Hz is just noise.
>
>
>
>             2012/8/2 Geoff                            >>
>
>
>                 if the geophone is OK then i understand
>                 the rdamp should be like 4x Rgeo.
>                 together the final R value is (Rd||Rg)
>                 the final Ge is like GRg/(Rd + Rg).
>                 If your geophone has a resistance
>                 more than like 1% off at room temperature
>                 you must consider it damaged somehow.
>                 Regards=2C
>                 geoff
>
>
>                 On 2012-07-30 14:34=2C Tiago A. wrote:
>
>                     Thanks for the answer Chris.
>
>                          I am not sure that I understand what you have
>             written - or what
>                     system you are using. What ADC / number of bits=2C
>             are you using ?
>
>                     The system (ADC) is a ADS1211P=2C the geophone is
>             connected
>                     directly to
>                     the ADC inputs with a 20cm wires. geIm using the
>             A/D set to
>                     22bits with
>
>                     the PGA set to 2x. With a Decimate Factor of 5600
>             with Turbo Mode 8=2C
>                     gives a sample rate of 27.86=2C which sets -3dB at
>             8Hz (3rd order
>                     digital
>                     filter) .
>
>                     You MUST damp a 1 Hz geophone correctly to get a
>             flat output
>                     over 1 Hz.
>                     What is the value of the damping resistor should i
>             use? Its a
>                     5500ohm
>                     geophone. But the strangest thing is i can only
>             measure 3800ohm
>                     (tested
>                     today)=2C i think when i got the geophone it had a
>             higher
>                     resistance. This
>                     geophone has be altered=2C the previous owner
>             changed the original
>                     Bendix
>                     6/8 pin connector to a 4 pin Bendix connector.
>
>                     How are you getting your period expansion below 1
>             Hz down to 0.1
>                     Hz ?
>                     Only using AmaSeis. One of the few times i could
>             get down to
>                     0.03Hz was
>                     in the Mexico M 7.4 earthquake (~7500km). It was
>             offline in the
>                     Sumatra
>                     earthquakes. I live in a small island in the
>             middle of the
>                     ocean=2C so i
>                     have always a lot of noise in the 2~5s period.
>
>                     What is the noise on your ADC - when you connect
>             it to a
>                     resistor with
>                     the same value as the geophone ?
>                     I can check that in the next days.
>
>
>                     Thanks.
>
>                     Regards=2C
>                     Tiago.
>
>
>
>                     2012/7/30                            >
>                                                >>>
>
>                          From: Tiago A. tiagoagre@.........
>             
>                                  >              
>
>                                  >>
>
>                          Sent: Mon=2C 30 Jul 2012 3:08
>                          Subject: High noise >10s
>                          Hi.
>
>                          Im using a L4 1Hz geophone and for almost a
>             month im
>                     struggling with
>                          high noise from 10s up to ...=2C but from <10s
>             it looks good. The
>                          noise comes and goes=2C this image is self
>             explaining:
>
>             http://dl.dropbox.com/u/__15802004/noise.png
>
>                     
>
>                          Changed cables=2C re centered the geophone=2C bu=
t
>             didint help..the
>                          geophone is connected directly to a ADC
>             without damping=2C
>                     external
>                          amplification or filtering=2C i only use
>             digital filtering
>                     from the
>                          ADC. Before this issue start=2C i had a pretty
>             clean spectrum
>                      >10s for
>                          almost 6 months=2C which allowed me to received
>             LQ and LR
>                     from some
>                          strong events.
>
>                          This sac contains 15minutes with high noise
>             >10s=2C notice
>                     that at
>                          3:37 it recorded a Ml2.1 at 70km.
>             http://dl.dropbox.com/u/__15802004/noise.sac
>
>                     
>
>                          Hi Tiago=2C
>                               I am not sure that I understand what you
>             have written
>                     - or what
>                          system you are using.
>                          You MUST damp a 1 Hz geophone correctly to
>             get a flat
>                     output over 1 Hz.
>                          How are you getting your period expansion
>             below 1 Hz down
>                     to 0.1 Hz ?
>                          Any period expansion DEPENDS on the geophone
>             being
>                     correctly damped.
>                          What is the noise on your ADC - when you
>             connect it to a
>                     resistor
>                          with the same value as the geophone ?
>                          You do need a low noise metal film resistor.
>                          What ADC / number of bits=2C are you using ?
>                          Regards=2C
>                          Chris Chapman
>
>
>
>
>               =20
>             ____________________________________________________________
>
>
>                 Public Seismic Network Mailing List (PSNLIST)
>
>                 To leave this list email
>             PSNLIST-REQUEST@..............
>             
>                              > with the body of
>             the message
>                 (first line only): unsubscribe
>                 See http://www.seismicnet.com/__maillist.html
>
>                  for more
>             information.
>
>
>
>         __________________________________________________________
>
>         Public Seismic Network Mailing List (PSNLIST)
>
>         To leave this list email PSNLIST-REQUEST@..............
>          with the body of the
>         message (first line only): unsubscribe
>         See http://www.seismicnet.com/maillist.html for more information.
>
>
>


  
    
  
  
    
Hello Tiago,

      

      You show an Artifact just over 1Hz.

      

      I have a similar artifact which seems related to

      air conditioner noise in the ground.

      

      But the artifact which bothers me is much more pure

      in frequency and is only present when the machine is running.

      

      I have vehicle noises 3Hz and over.

      They vary all the time.

      

      If you are like me, you are 800feet over bedrock which

      means no roads should be within 800 ft of your

      geophone. Impossible for me to do.

      

      But the Air Conditioners in the buildings around me

      as well as my own causes terrible artifacts which can

      Jam out all other frequencies by overloading

      the preamp driving it into saturation or cutoff.

      My air conditioner rests upon the ground.

      Living in the desert without an air conditioner

      is almost unthinkable to computer people

      unless you have a cray supercomputer.

      (They got their own way to keep cool.)

      

      I fight these artifacts in two ways.

      

      1. Filter Low Pass n=1 at 12 second period.

      2. Filter again n=1 low pass at geophone f0 of 1.0Hz to 1.75Hz.

      3.Antialize LP n=4 at like 4 to 10 Hz.

      4. use sample rate of 100Hz

      

      Another way which seems to help but i do not like

      is to dampen very heavily and compensate with

      a N=1 LPF at like 12 seconds.

      If you do this you need more gain, like 50Dbv more.

      

      The way to look at noise is to pass your geophone signal

      straight through to the A/D with no filtering

      and only amplify to like -6.0Dbv the pure noise.

      

      Then make recording samples over 24 hours.

      

      Convert the 1Hr samples to Wave and look at the profiles in

      Audacity. You need a FFT program which shows

      changes with time so you can see if the

      artifacts are constant or variable.

      

      The FFT within Winquake is just an overall profile

      and building a waterfall from it is kind of hard.

      

      Audacity is free, and I or possibly another PSN person

      can supply you with a PSN to WAVE converter program.

      This all hinges on the fact you are an amateur and not a

      commercial person. Trying to make a living doing this.

      These programs like Audacity are generally not free

      to commercial enterprises generating revenue.

      The people who write these programs want a

      so to speak piece of the action.

      

      My current setup is not exactly as I say here.

      I am always looking for something better.

      

      Good luck.

      

      Regards,

      geoff

      

      

      

      On 8/9/2012 2:05 AM, Tiago A. wrote:

    
    
Forgot the picture to compare noise before/now:

      

      http://dl.dropbox.com/u/15802004/com.png

      

      
2012/8/9 Tiago A. <tiagoagre@.........>

        
Thanks for
          the answer Geoff.

          

          I´m not using Larrys Boards (yet), im using a ADC ADS1211P
          mounted in a PCB, image:

          http://imageshack.us/photo/my-images/31/adca.jpg/

          

          The board worked ok for almost a year.

          

          Hadnt much time to test more the noise, but here is a picture
          which shows very well the issues:

          First image - 3 months back. 0.25Hz to 0.75Hz is ocean noise.

          Second image - Taken few minutes ago.

          

          

          >10s noise is probably 10 times higher than before, also i
          have some high count at a specific frequencies, starts at
          +-1Hz, next day 2Hz, next day 3Hz). Restart the board/Amaseis,
          the high count returns to +-1Hz. 

          

          I will follow your advices and i will search some noise
          sources.

          

          Best Regards,

          Tiago.
          

            


              

              
2012/8/8 GMVoeth GM <gmvoeth@.........>

                
Sorry
                  Tiago,

                  

                  I can not now handle SAC files.

                  

                  The only kind of files I handle are PSN.

                  

                  I recommend you change sample rates, Assuming you are
                  using Larrys Type III A/D board.

                  

                  Then you create a test file, convert to WAVE both
                  before and after sample rate change files.

                  

                  Then look at the results in Audacity FFT Waterfall
                  program.

                  

                  This is the only way i know how to evaluate such a
                  problem.

                  

                  You talk about things I know nothing about like
                  (sample rate to 125sps (-3dB at 36Hz)).

                  

                  (-3dB at 36Hz) means to me a Low Pass Filter At 36Hz.

                  

                  If you filter at 36 hZ your sample rate should be much
                  higher than 100

                  more like 500 sps.

                  

                  You need to filter out even frequencies above the
                  rolloff.

                  

                  When you mix frequencies you get the following,

                  

                  F1 & F2 (Fundamentals),

                   F1 + F2 (SUM), and,

                   F1 - F2 (Difference).

                  

                  You will notice small variations in the fundamentals

                  can result in large changes at higher harmonics.

                  

                  

                  

                  I am assuming that when you get alizing you are
                  getting these mixing products.

                  

                  Frequency mixing is typical for superhetrodyne
                  receivers.

                  

                  If your problem is not mixing you need to

                  look at everything else like staic electricity,

                  Commom mode rejection, Thermal variations.

                  

                  Like take a soda straw and carefully blow your warm
                  breath on

                  various components to see what causes changes.

                  Do this while recording.

                  

                  It took me a long time to get rid of most artifacts.

                  

                  The best thing I did was buy a manufactured (used)
                  geophone

                  then lower the overall gain of my system.

                  

                  If you need more than x10000, little problems can
                  easily be big ones.

                  

                  I was unable to stop unwanted artifacts if gain was
                  over X100,000.

                  

                  Good Luck Comrade,

                  Regards,

                  geoff
                  


                    

                    

                    

                    On 8/2/2012 4:19 PM, Tiago A. wrote:

                  
                  

                    

                      Hi Geoff.

                      

                      Increasing the sample rate to 125sps (-3dB at
                      36Hz), didint solve the

                      issue and increased the >10s noise..i will try
                      to increase more the

                      sample rate. But increasing the sample rate
                      reveals a very high count at

                      50Hz, i check the earth connections it looks all
                      ok..if i remove the

                      geophone from the ADC, i have +-2 counts of noise
                      at 16bits and the 50Hz

                      spike is gone. Simply touching a wire from earth
                      in any part of the

                      geophone, will make the geophone stiff, without
                      responding.

                      

                      SAC file with 15minutes at 125SPS

                      http://dl.dropbox.com/u/15802004/aa.sac

                      

                      Netherless the 50Hz issue, getting only 3800ohm
                      from a 5500ohm geophone

                      is a good indicator that something is wrong with
                      the geophone itself. It

                      still responds ok to >0.1Hz, but <0.1Hz is
                      just noise.

                      

                      

                      

                    
                    2012/8/2 Geoff <gmvoeth@.........
                    <mailto:gmvoeth@.........>>
                    

                      


                        

                            if the geophone is OK then i understand

                            the rdamp should be like 4x Rgeo.

                            together the final R value is (Rd||Rg)

                            the final Ge is like GRg/(Rd + Rg).

                            If your geophone has a resistance

                            more than like 1% off at room temperature

                            you must consider it damaged somehow.

                            Regards,

                            geoff

                        

                        

                            On 2012-07-30 14:34, Tiago A. wrote:

                        

                                Thanks for the answer Chris.

                        

                                     I am not sure that I understand
                        what you have written - or what

                                system you are using. What ADC / number
                        of bits, are you using ?

                        

                                The system (ADC) is a ADS1211P, the
                        geophone is connected

                                directly to

                                the ADC inputs with a 20cm wires. geIm
                        using the A/D set to

                                22bits with

                        

                                the PGA set to 2x. With a Decimate
                        Factor of 5600 with Turbo Mode 8,

                                gives a sample rate of 27.86, which sets
                        -3dB at 8Hz (3rd order

                                digital

                                filter) .

                        

                                You MUST damp a 1 Hz geophone correctly
                        to get a flat output

                                over 1 Hz.

                                What is the value of the damping
                        resistor should i use? Its a

                                5500ohm

                                geophone. But the strangest thing is i
                        can only measure 3800ohm

                                (tested

                                today), i think when i got the geophone
                        it had a higher

                                resistance. This

                                geophone has be altered, the previous
                        owner changed the original

                                Bendix

                                6/8 pin connector to a 4 pin Bendix
                        connector.

                        

                                How are you getting your period
                        expansion below 1 Hz down to 0.1

                                Hz ?

                                Only using AmaSeis. One of the few times
                        i could get down to

                                0.03Hz was

                                in the Mexico M 7.4 earthquake
                        (~7500km). It was offline in the

                                Sumatra

                                earthquakes. I live in a small island in
                        the middle of the

                                ocean, so i

                                have always a lot of noise in the 2~5s
                        period.

                        

                                What is the noise on your ADC - when you
                        connect it to a

                                resistor with

                                the same value as the geophone ?

                                I can check that in the next days.

                        

                        

                                Thanks.

                        

                                Regards,

                                Tiago.

                        

                        

                        

                                2012/7/30 <chrisatupw@.......
                        <mailto:chrisatupw@.......>

                      
                    
                            <mailto:chrisatupw@.......
                    <mailto:chrisatupw@.......>>>

                    

                                 From: Tiago A. tiagoagre@.........

                            <mailto:tiagoagre@.........>
                    <mailto:tiagoagre@.........
                    


                              <mailto:tiagoagre@.........>>

                      

                                   Sent: Mon, 30 Jul 2012 3:08

                                   Subject: High noise >10s

                                   Hi.

                      

                                   Im using a L4 1Hz geophone and for
                      almost a month im

                              struggling with

                                   high noise from 10s up to ..., but
                      from <10s it looks good. The

                                   noise comes and goes, this image is
                      self explaining:

                      

                    
                            http://dl.dropbox.com/u/__15802004/noise.png
                    


                              <http://dl.dropbox.com/u/15802004/noise.png>

                      

                                   Changed cables, re centered the
                      geophone, but didint help..the

                                   geophone is connected directly to a
                      ADC without damping,

                              external

                                   amplification or filtering, i only
                      use digital filtering

                              from the

                                   ADC. Before this issue start, i had a
                      pretty clean spectrum

                               >10s for

                                   almost 6 months, which allowed me to
                      received LQ and LR

                              from some

                                   strong events.

                      

                                   This sac contains 15minutes with high
                      noise >10s, notice

                              that at

                                   3:37 it recorded a Ml2.1 at 70km.

                    
                            http://dl.dropbox.com/u/__15802004/noise.sac
                    


                              <http://dl.dropbox.com/u/15802004/noise.sac>

                      

                                   Hi Tiago,

                                        I am not sure that I understand
                      what you have written

                              - or what

                                   system you are using.

                                   You MUST damp a 1 Hz geophone
                      correctly to get a flat

                              output over 1 Hz.

                                   How are you getting your period
                      expansion below 1 Hz down

                              to 0.1 Hz ?

                                   Any period expansion DEPENDS on the
                      geophone being

                              correctly damped.

                                   What is the noise on your ADC - when
                      you connect it to a

                              resistor

                                   with the same value as the geophone ?

                                   You do need a low noise metal film
                      resistor.

                                   What ADC / number of bits, are you
                      using ?

                                   Regards,

                                   Chris Chapman

                      

                      

                      

                      

                    
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